What is School Cake? It’s a basic vanilla sponge cake recipe with water icing and sprinkles. We have sometimes seen it sliced in two horizontally with jam in the middle, but mostly it’s just as is! It often came served with custard too. School Cake has a few different names. Sometimes it’s called Old School Cake, Retro School Cake, School Dinner Cake, School Cake Traybake, sometimes literally Sponge Cake with Sprinkles, Sprinkle Sponge, or Sprinkle Cake. Whatever you call it, it's simple to make and delicious!